I/O Drive Ratio

[FreeBeeTony]

What is the ratio of the drive that mates to a 470 Merc? I have a 165HP Merc 250 cui IL6, I believe the ratio needed here is 1.65:1. Hope the 470 has the same ratio as I can get a drive off a 470 very cheap and I don't have a drive at all at the moment. If the ratio is different, is it possible to compensate for a different ratio by adjusting the prop pitch to achieve the same RPM's? I am obviously trying to save some $. I just bought a project boat that needs a drive and it looks like I can get one off a 470 for next to nothing. If I can't use this ratio, how difficult is it to change the gears?

 

[FreeBeeTony]

Re: I/O Drive Ratio

BUMP^

 

[Trent]

Re: I/O Drive Ratio

Small block V-8's usually have ratios of 1.50:1 and 1.47:1<br />V-6 engines and older in-line 6 cyl engines use 1.65:1 ratios.<br />In-line 4 cylinder engines will use a 1.98:1 or a 1.84:1 ratio drive.<br /><br />Not to hard to change the gears, But if you have never done it before I would pay someone to do it.<br /><br />Note: Mercrusier updated their lower gear sets some time back and it changed the gear ratios.<br /><br />What was a 1.50:1 is now a 1.47:1<br />What was a 1.65:1 is now a 1.62:1<br />What was a 1.84:1 is now a 1.81:1<br />What was a 1.98:1 is now a 1.94:1

 

[FreeBeeTony]

Re: I/O Drive Ratio

Thanks Trent, but that doesn't answer my question. Can the prop pitch be used to compensate for a different outdrive gear ratio?

 

[Bondo]

Re: I/O Drive Ratio

Yes, Tony......<br />The 1.84/1 is used on the I6... The 1.65/1 is used for the V6... The 1.50/1 is used for the V8s... And the 1.98/1 is used for the I4s(120hp+140hp)... The 470s can be found with Both the 1.84/1, Or the 1.98/1... Odds are the one you have is the 1.84/1, Which IS the ratio you need for the I6.... Either way,there are About 4", to 6"s of pitch between the ratios.... A single ratio shift can be made-up in pitch, Two ratios difference will get you either up-pitch, or down-pitch so much that props in the needed pitches are Very Hard to Find....